Hitherto, a seat belt apparatus equipped in a vehicle, such as an automobile, prevents an occupant from being thrown out from the seat in an emergency described above by restricting the occupant with a seat belt.
Such a seat belt apparatus is provided with a seat belt retractor that retracts the seat belt. In such a seat belt retractor, when the seat belt is not worn, the seat belt is retracted in a spool, and when worn, the seat belt is withdrawn and is worn by an occupant. Furthermore, in an emergency such as the one described above, withdrawal of the seat belt is prevented by an operation of a lock mechanism of the seat belt retractor preventing rotation of the spool in a seat belt withdrawing direction. With the above, in an emergency, the seat belt restricts the occupant.
Incidentally, in the above known seat belt retractor of the seat belt apparatus, when the seat belt restricts the occupant in an emergency, such as in a vehicle collision, since a rapid vehicle deceleration occurs, the occupant is made to move forward due to a large inertia. Accordingly, a large load is applied to the seat belt and a large energy is applied to the occupant by the seat belt. The energy is not particularly a problem to the occupant but, if possible, it is desirable that the energy is restricted.
Accordingly, conventionally, a seat belt retractor has been developed that is provided with a torsion bar so that, in a state in which the seat belt is worn and in an emergency, the load acting on the seat belt is restricted and energy is absorbed.
However, in conventional seat belt retractors, only a single limit load is set for the limit load after the collision. In actuality, the energy applied to the occupant differs in various manners depending on the weight and the like of the occupant. Rather than responding to such a large energy that differ variously with a single limit load, by setting limit loads according to the circumstances of the vehicle in an emergency, the occupant can be restricted in a more effective and adequate manner.
Accordingly, seat belt retractors that are capable of setting various limit loads applied to the seat belt have been proposed (see Patent Literature 1 and Patent Literature 2, for example).
The seat belt retractors disclosed in Patent Literature 1 and Patent Literature 2 are each provided with two EA mechanisms each having a different EA characteristics, and one or two EA mechanisms are operated according to the state of the emergency. As described above, by selectively operating the two EA mechanisms according to the state of the emergency as appropriate, the limit load applied to the seat belt can be set in two stages.